Some self-traveling vehicles include an object detecting means for detecting an object in the traveling direction of the vehicle and the distance from the vehicle to the object, and a speed control actuator. Others further include a course storage means for storing a predetermined course in a coordinate system and a current position defining means for receiving coordinate information on the predetermined course from the course storage means and defining a current position of a vehicle on the predetermined course.
The object detecting means transmits a directional medium, such as light, a millimeter wave, or an ultrasonic wave, in the traveling direction of a vehicle. A reflected wave from an object is received and the transmitted and received waves are processed to detect the object. Also, various means of determining a distance to the object and relative velocity with respect to the object are known. In a millimeter-wave method, for example, a signal wave (usually a chopping wave) together with a millimeter wave is transmitted from a transmitting antenna in the traveling direction of a vehicle. A reflected wave from the object is received by a receiving antenna, and the transmitted and received waves are processed by a pulse method, a two frequency CW method, a FM-CW method or the like. In addition, a method in which more than one object is detected at the same time as well as each distance and the relative speed of each object, by means of a frequency analysis method such as a filter bank or a fast Fourier transform (FFT) is known. Incidentally, objects to be detected are usually other vehicles traveling ahead of the vehicle in the traveling direction which can be obstacles to the vehicle. However, if a directional medium is transmitted without limits, objects such as road surfaces, telegraph poles on road shoulders, guardrails, various kinds of road signs, buildings beyond curves, or steep cliffs are detected. To prevent these undesired detections, in a millimeter-wave system, for example, the area of an antenna, the antenna height, the antenna angle (which is the illuminating angle), the output intensity of the millimeter wave, the frequency of the millimeter wave, the signal wave, and the like are adjusted so that a forward detection limit is set for about 150 meters, for example, and a detection limit in vertical and lateral directions will be set for about four meters (corresponding to the width of one road lane), for example. Thus, for example, devices are provided which do not detect objects outside a straight course of travel and do not mistake a road surface for a detected object by regarding a reflected wave from the road surface itself as noise or ground clutter, and the like. In a situation wherein an object is on an uphill road, a wave is reflected from the uphill road or the object and is received. However, the reflection intensity from the uphill road is usually larger than the reflection intensity from a flat road (corresponding to the aforementioned noise or ground clutter), but smaller than reflection intensity from the object on the uphill road. In addition, if a graph is constructed with a vertical axis indicating the reflected wave intensity and a horizontal axis indicating distance, the reflection intensity from the uphill road continuously increases as the distance increases. Conversely, in the case of a flat road, the reflection intensity becomes smaller as the distance increases. Therefore, the presence or absence of an uphill road, or art object on the uphill road, is discriminated.
The speed control actuator consists of a means to control the vehicle speed, such as an accelerator, a brake or the like. In a manually operated vehicle, the speed control actuator is operated by an operator. In an unmanned vehicle traveling on a predetermined course, a speed control program, corresponding to the predetermined course, is stored in advance, and the speed control actuator is automatically controlled in accordance with the speed control program.
The course storage means is a memory for storing a shape of a predetermined course in a coordinate system for a vehicle traveling on a predetermined course (an unmanned vehicle, for example). Storage information, such as the distance of each section, course width, curves, downhill roads, uphill roads, gradients, and the like, are outputted to be used in computations.
The current position defining means receives coordinate system information on the predetermined course from the course storage means and defines a current position of a vehicle on the predetermined course. For example, a gyro, an equipment disposed at every important position in the course for giving and receiving position information to/from a vehicle, GPS using an artificial satellite, or the like are used.
Incidentally, technology disclosed in Japanese Patent Laid-open No. 5-203746 can be embodied in a self-traveling vehicle including some of the aforementioned factors. This technology detects the distance between two vehicles and provides an alarm device for changing a detection area by laser beam according to a radius of curvature of a curve as detected by a steering sensor.
However, a detection limit of the object detecting means and an effective detection limit of a vehicle are different. In the case of curves or downhill roads, for example, the effective detection limit of the vehicle itself becomes shorter. Specifically, in a curve, the detection limit area of the object detecting means includes the area beyond the curve; however, the effective detection limit of the vehicle is up to the outer edge of the curve in the detection limit area. In such a case, the effective detection limit is shorter than the detection limit of the object detecting means. Moreover, on a downhill road in a traveling direction, other vehicles or the like cannot at time be detected, depending on the gradient of the downhill road, since they are located below a lower surface of the detection limit area. Also, in such a case, the effective detection limit is shorter than the detection limit of the object detecting means. In the above cases, if a vehicle travels at such a speed that the vehicle cannot stop within the effective detection limit, the vehicle will collide or interfere with another vehicle, even if the object detecting means applies the brakes to the vehicle immediately after detecting an obstacle. Technology wherein an effective detection limit is connected with vehicle speed, as described above, is not known in the art. The technology disclosed in the aforementioned Japanese Laid-open Patent No. 5-203746 is useful only for discriminating between obstacles outside a course of travel and obstacles inside the course of travel. Specifically, when vehicle speed is left to an operator, collision or interference can be prevented, but there is some risk of collision or interference due to inattention of the operator. On the other hand, in a self-traveling vehicle, which stores a speed control program corresponding to a predetermined course and travels on the predetermined course in accordance with the speed information defined in the speed control program, such as an unmanned dump truck working in mines, or the like, a vehicle speed capable of preventing collision or interference with a detected object in any condition is set and the vehicle travels on the predetermined course in accordance with the set speed. In this case, the set speed is slow, thereby securing safety but making it difficult to improve productivity.